(a) Field of the invention:
The present invention relates to an improvement of the IC tester socket which is suitable for use in the performance test of a flat type IC (Integrated Circuit) having curved lead terminals and like testing.
(b) Description of the prior art:
Flat type IC tester sockets have been constructed in the past so that, as shown in FIG. 1, by urging, via an urging member A, the bottom face RF of a lead terminal R of an IC package (note: in actual practice, a face connected to, for example, the circuit line of the printed circuit board) to a top face CF for contact of a contacting pin C attached to an electrically insulated socket body B, the connection of the lead terminal R with the contacting pin C is established.
With the above-mentioned structure, however, the contact face RF of the lead terminal R of the IC package P tends to be injured easily, and moreover there occurs deposition of dust onto this contact face, and furthermore, dust could fill in the space existing therearound. In such a case, it should be noted that, in a compact-size IC package P, the pitch size between adjacent lead terminals R is very small, and accordingly it is difficult to easily remove the dust which has deposited onto the lead terminal portions. Especially, in case of such dust that cannot be found with the naked eye, there would arise the risk that the IC package bearing unnoticeable dust is shipped as being an acceptable product in the performance test. However, when, in actual practice, such an IC package as mentioned above is mounted on a printed circuit board and soldered, it would cause poor soldering, or even when the IC package is soldered once to the printed circuit board, the soldered portion would come off at a later date and develop a disorder in the connection, causing the IC-mounted hardwares to become inoperative. Also, in such a case as mentioned above, it is the general trend that the circuitry is compact in size and complex, so that it is extremely difficult to check and find the bad spot, and a lot of time is required for inspection. In order to preliminarily prevent such disorder and trouble from taking place, a close inspection step has to be introduced before the assembling step.
In order to solve the above-mentioned problems, there has been proposed a tester socket which is constructed so that the contacting pins are brought into contact with the side faces of the lead terminals (U.S. Pat. No. 4,491,377). FIGS. 2A and 2B show an example of such a tester socket. More particularly, the contacting pin C has its upper portion made in a bifurcated fork shape and has a downwardly and inwardly extending slant top face C.sub.1, and has its lower portion inserted in the socket body B. An urging member A, when viewed from thereabove along the arrow in FIG. 2A, is of a square frame shape whose central portion is open, and is attached to the socket body B via guide columns G for vertical movement. Inside this urging member A, there is formed an inclined face A.sub.1 which is brought into a sliding contact with the slant top face C.sub.1 of the contacting pin C. This contacting pin C is flat in shape and is so made that elastic force acts upon it in a direction to cause the respective arms of its bifurcated fork portion to part away from each other. The magnitude of the elastic force is selected to be in the level of being able to hold the urging member A in its position of FIG. 2A against its own gravity in the relaxed position thereof in FIG. 2A. FIG. 2A shows the state that an IC package P which requires testing is placed in position through the central opening or cavity of the urging member A. In this state, by downwardly pushing the urging member A in the direction of the arrow, the slant top face C.sub.1 of the contacting pin C is urged by the inclined face A.sub.1 of the urging member A, causing the inner arm of the fork thereof to be displaced to the tensioned position of FIG. 2B. As a result, the IC package P drops onto the position it is received by the socket body B and rests thereat. In this state, by relieving the urging force applied to the urging member A, the tensioned fork arm tends to return to its relaxed position by its own restoring force. However, because the side face C.sub.2 of the fork arm is in pressure-contact with the side face R.sub.1 of the lead terminal R, the fork arm is forced to stop in this position, and accordingly the IC package P is rendered to the state of being nipped at both sides by the contacting pins C. Thus, when various kinds of test have been completed, the urging member A is pressed downwardly again. Whereupon, the IC package P can be taken out easily. By subsequently releasing the pressure applied to the urging member A, both the contacting pins and the urging member restore their respective positions shown in FIG. 2A.
Now, sockets of this type, in general, are small in the size of the whole body and accordingly the contacting pins are made thin and small in size. The conventional socket having the above-described improved sturuture is of such an arrangement that a markedly heavy load is forced to be applied to a portion of the contacting pin, i.e. a structure that one of the fork arms of the respective contacting pins is forced to exert the following two functions, one of which is to support the urging member and the other is to hold the contact pressure applied to the mating lead terminal. Hence, there is the drawback that the contacting pins tend to become fatigued easily, and that according they cannot stand their use for an extended period of time. In other words, when the base portion of the fork arm becomes fatigued, it immediately develops mal-contact so that the tester socket will become unusable. Also, in the tester socket having the abovedescribed conventional structure, its contact pins do not have a configuration which makes it possible to maintain a sufficient and proper elastic force.